Method and arrangement in a telecommunication system

ABSTRACT

The downlink control channels in a control region of each downlink subframe in a telecommunication system are divided into at least one common subset of the downlink control channels and a plurality of group subsets of the downlink control channels, such that the common subset or each common subset will be decoded by every user equipment, and each group subset will be decoded only by a limited group of user equipments. Resource assignment messages for a user equipment can then be transmitted on a downlink control channel of the relevant group subset, to avoid the need for messages to be decoded by a large number of UEs that will not act on them, while broadcast messages can be transmitted on a downlink control channel of the relevant common subset, to avoid the need for messages to be transmitted many times.

RELATED APPLICATIONS

This application claims priority and benefit from InternationalApplication No. PCT/SE2008/051275, filed on Nov. 7, 2008, which claimspriority to U.S. Provisional Application No. 61/015,347, filed on Dec.20, 2007, the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

This invention relates to a method and arrangement in atelecommunication system, and in particular to a method for allocatingdownlink control channels to user equipments.

BACKGROUND

Evolved UTRAN (E-UTRAN), sometimes also referred to as LTE (Long TermEvolution), is a novel radio access technology being standardized by the3rd Generation partnership Project (3GPP). Only the packet-switched (PS)domain will be supported in E-UTRAN, i.e. all services are to besupported in the PS domain. The standard will be based on OFDM(Orthogonal Frequency Division Multiplexing) in the downlink and SC-FDMA(Single Carrier Frequency Domain Multiple Access) in the uplink.

In the time domain, one subframe of 1 ms duration is divided into 12 or14 OFDM (or SC-FDMA) symbols, depending on the configuration. One OFDM(or SC-FDMA) symbol consists of a number of subcarriers in the frequencydomain, depending on the channel bandwidth and configuration. One OFDM(or SC-FDMA) symbol on one subcarrier is referred to as a ResourceElement (RE).

In E-UTRAN no dedicated data channels are used; instead, shared channelresources are used in both downlink and uplink. These shared resources,DL-SCH (Downlink Shared Channel) and UL-SCH (Uplink Shared Channel), arecontrolled by one or more schedulers that assign different parts of thedownlink and uplink shared channels to the UEs for reception andtransmission respectively.

The assignments for the DL-SCH and the UL-SCH are transmitted in acontrol region covering a few OFDM symbols in the beginning of eachdownlink subframe. The DL-SCH is transmitted in a data region coveringthe rest of the OFDM symbols in each downlink subframe. The size of thecontrol region is either one, two, three or four OFDM symbols and is setper subframe.

Each assignment for DL-SCH or UL-SCH is transmitted on a physicalchannel named PDCCH (Physical Downlink Control Channel). There aretypically multiple PDCCHs in each subframe and the UEs will be requiredto monitor the PDCCHs to be able to detect the assignments directed tothem.

Groups of resource elements that can be used for the transmission ofcontrol channels are referred to as Control Channel Elements (CCEs), anda PDCCH is mapped to a number of CCEs. For example, a PDCCH consists ofan aggregation of 1, 2, 4 or 8 CCEs. A PDCCH consisting of one CCE isreferred to as a PDCCH at aggregation level 1, a PDCCH consisting of twoCCEs is referred to as a PDCCH at aggregation level 2, and so on. EachCCE may only be utilized on one aggregation level at a time. Thevariable size achieved by the different aggregation levels is used toadapt the coding rate to the required block error rate (BLER) level foreach UE. The total number of available CCEs in a subframe will varydepending on several parameters, such as the number of OFDM symbols usedfor the control region, the number of antennas, the system bandwidth,the PHICH (Physical HARQ Indicator Channel) size etc.

Each CCE consists of 36 REs. However, in order to achieve time andfrequency diversity for the PDCCHs, each CCE and its REs are spread out,both in time over the OFDM symbols used for the control region, and infrequency over the configured bandwidth. This is achieved through anumber of operations including interleaving, and cyclic shifts etc.These operations are however predefined, and are completely known to theUEs. That is, each UE knows which resource elements make up each CCE,and is therefore able to decode the relevant resource elements in orderto decode any desired PDCCH.

The existing system has the disadvantage that, as UEs have no knowledgeof where the PDCCHs directed specifically to them are located, each UEhas to decode the entire set of possible PDCCHs, i.e. the entire PDCCHspace. The entire PDCCH space includes all CCEs on all aggregationlevels. This would mean that considerable UE resources are consumed indecoding a large number of PDCCHs, of which only a few were actuallydirected to them. This will waste the limited UE battery power and hencereduce the UE stand-by time.

SUMMARY

According to a first aspect of the present invention, there is provideda method of allocating communications resources in a telecommunicationsystem, in which the assignments of resources to user equipments aretransmitted in a control region of each downlink subframe, the controlregion comprising a plurality of downlink control channels. The downlinkcontrol channels are divided into at least one common subset of thedownlink control channels and a plurality of group subsets of thedownlink control channels, thereby enabling every user equipment todecode the common subset and only one group subset.

According to a second aspect of the present invention, there is provideda method of operation of a user equipment in order to determinecommunications resources allocated thereto in a telecommunicationsystem, in which the assignments of resources to user equipments aretransmitted in a control region of each downlink subframe, the controlregion comprising a plurality of downlink control channels. A divisionof the downlink control channels into at least one common subset of thedownlink control channels and a plurality of group subsets of thedownlink control channels is determined, and a relevant group subsetfrom the plurality of group subsets is determined. The downlink controlchannels forming the common subset or each common subset of the downlinkcontrol channels are decoded, and only the downlink control channels ofthe relevant group subset of the downlink control channels are decoded.

According to a third aspect of the present invention, there is provideda network node for a telecommunication system, in which the assignmentsof resources to user equipments are transmitted in a control region ofeach downlink subframe, the control region comprising a plurality ofdownlink control channels. The network node divides the downlink controlchannels into at least one common subset of the downlink controlchannels and a plurality of group subsets of the downlink controlchannels, enabling every user equipment to decode the common subset andonly one group subset.

According to a fourth aspect of the present invention, there is provideda user equipment in a telecommunication system, in which the assignmentsof resources to user equipments are transmitted in a control region ofeach downlink subframe, the control region comprising a plurality ofdownlink control channels. The user equipment determines communicationsresources allocated to it by determining a division of the downlinkcontrol channels into at least one common subset of the downlink controlchannels and a plurality of group subsets of the downlink controlchannels; and determining a relevant group subset from the plurality ofgroup subsets. The user equipment than decodes the downlink controlchannels forming the common subset or each common subset of the downlinkcontrol channels, and decodes only the downlink control channels of therelevant group subset of the downlink control channels.

This has the advantage that the number of possible PDCCHs that have tobe decoded by each UE is reduced. This is achieved by dividing the PDCCHspace into a number of subsets where each UE only has to decode PDCCHsfrom certain subsets.

A subset is defined as a specific set of possible PDCCHs. A commonsubset is a subset which all UEs shall try to decode. A group subset isa subset which only a limited group of UEs shall try to decode. Theexact number of subsets of each type could differ. Also, how thesesubsets are formed with respect to CCE indices, and aggregation level ofCCEs into PDCCHs, could differ.

One potential problem that could arise from introducing subsets of thecontrol channels, and requiring each UE to decode only one subset isthat some PDCCH messages will be broadcast to all UEs in the cell, e.g.the SIB (System Information Block) sent on the BCCH (Broadcast Channel).For broadcast messages, the same DL-SCH assignment would have to be sentin every subset in order to reach all UEs. This would mean a waste ofthe CCE resources.

Another problem with subsets is that the pooling gain with one big poolof CCEs is lost when dividing the resources into a number of subsets. Ifall UEs are assigned to one subset during one subframe, the CCEresources in the other subsets are lost and the system throughput couldsuffer.

However, according to the present invention, the disadvantage of theprior art is at least partially obviated, and these new potentialdisadvantages are not introduced. It is thus the basic idea of thepresent invention to reduce the number of PDCCHs that a UE has to decodewithout introducing severe restrictions leading to problems as describedabove. This is achieved by dividing the entire set of possible PDCCHsinto a number of group and common subsets respectively. Each groupsubset is decoded by a limited group of 0, 1 or more UEs, whereas thecommon subset, preferably there is only one, is decoded by every singleUE. The formation of the subsets is performed in such a way that neitherCCE resources have to be wasted in case of broadcasting nor that CCEsare virtually lost for group subsets where the CCE resources are notutilized.

The present invention therefore makes it possible to save UE batterypower without preventing the eNodeB from utilising the complete CCEspace. Further, the invention allows for an efficient usage of CCEs incase of broadcast messages.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a representation of a part of amobile communications network operating in accordance with an aspect ofthe present invention.

FIG. 2 illustrates one possible division of one downlink subframe intime and frequency.

FIG. 3 is a first flow chart, illustrating a method performed in anetwork node in accordance with an aspect of the present invention.

FIG. 4 is a second flow chart, illustrating a method performed in a userequipment in accordance with an aspect of the present invention.

FIG. 5 is a schematic diagram, illustrating a division of the PDCCHspace.

DETAILED DESCRIPTION

FIG. 1 shows a part of a mobile communications network operating inaccordance with an aspect of the present invention. This illustratedembodiment refers to a network operating in accordance with the EvolvedUMTS Terrestrial Radio Access (E-UTRA) standards defined by the 3GPPorganization. However, it will be appreciated that the invention may beapplied to any network involving allocation of shared resources on asystem downlink.

Specifically, FIG. 1 shows a basestation, or eNodeB, 10 in a cell of acellular network in the form of an Evolved Radio Access Network. In theillustrated embodiment of the invention, the network operates inaccordance with a standard based on OFDM (Orthogonal Frequency DivisionMultiplexing) in the downlink and SC-FDMA (Single Carrier FrequencyDomain Multiple Access) in the uplink. FIG. 1 also shows four UEs 12,14, 16, 18 located within the cell served by the eNodeB 10.

Specifically, FIG. 1 illustrates the general form of the eNodeB 10. TheeNodeB 10 has radio frequency (RF) interface circuitry 102, connected toan antenna 104, for transmitting and receiving signals over a wirelessinterface to the UEs. In addition, there is a core network (CN)interface 106, for connecting the eNodeB 10 to a core network of themobile communications network. The radio frequency interface circuitry102 and the core network interface 106 operate under the control of aprocessor 108. This is generally well understood, and will not bedescribed further herein. In particular, the processor 108 isresponsible for allocating signals to the available communicationsresources, which in this illustrative network comprise resources onparticular frequency subcarriers during particular time periods. Theprocessor 108 is also responsible for transmitting resource allocationmessages to the UEs. One aspect of such control is relevant for anunderstanding of the present invention, and is described in more detailbelow.

FIG. 1 also illustrates the general form of one UE 12, it beingunderstood that the other UEs are generally similar. The UE 12 has radiofrequency (RF) interface circuitry 122, connected to an antenna 124, fortransmitting and receiving signals over the wireless interface to theeNodeB 10. The radio frequency interface circuitry 122 operates underthe control of a processor 126. This is generally well understood, andwill not be described further herein. In particular, the processor 126is responsible for controlling the RF interface circuitry 122, in orderto ensure that the intended signals are decoded, and that signals fortransmission are applied to allocated communications resources.

FIG. 2 illustrates the form of one subframe. As is well known, asubframe of duration 1 ms is divided into 12 or 14 OFDM (or SC-FDMA)symbols, depending on the configuration, and in this example thesubframe is divided into 14 OFDM symbols. In the frequency domain, theavailable bandwidth is divided into subcarriers, depending on thechannel bandwidth and configuration. One OFDM (or SC-FDMA) symbol on onesubcarrier is referred to as a Resource Element (RE). Certain predefinedResource Elements are used for transmitting reference symbols 20.

Shared channel resources are used in both downlink and uplink, and theseshared resources, DL-SCH (Downlink Shared Channel) and UL-SCH (UplinkShared Channel), are each controlled by one scheduler that assignsdifferent parts of the downlink and uplink shared channels to differentUEs for reception and transmission respectively.

The assignments for the DL-SCH and the UL-SCH are transmitted in acontrol region covering a few OFDM symbols in the beginning of eachdownlink subframe. The size of the control region is either one, two,three or four OFDM symbols and is set per subframe. The size of thecontrol region for a specific subframe is indicated by the ControlFormat Indicator (CFI) which is carried by the Physical Control FormatIndicator Channel (PCFICH) in the very first OFDM symbol of the samesubframe. In the illustrated example shown in FIG. 2, the control regioncovers the first three OFDM symbols in the subframe. The DL-SCH istransmitted in a data region covering the rest of the OFDM symbols ineach downlink subframe. Thus, in this example, the data region coversthe last eleven OFDM symbols in each downlink subframe.

Each assignment for DL-SCH or UL-SCH is transmitted on a physicalchannel named PDCCH (Physical Downlink Control Channel). There aretypically multiple PDCCHs in each subframe and the UEs 12, 14, 16, 18will be required to monitor the PDCCHs to be able to detect theassignments directed to them.

A PDCCH is mapped to a number of CCEs (Control Channels Elements). APDCCH consists of an aggregation of 1, 2, 4 or 8 CCEs. These fourdifferent alternatives are herein referred to as aggregation levels 1,2, 4, and 8 respectively. Each CCE may only be utilized on oneaggregation level at a time. The variable size achieved by the differentaggregation levels is used to adapt the coding rate to the required BLERlevel for each UE. The total number of available CCEs in a subframe willvary depending on several parameters, such as the number of OFDM symbolsused for the control region, the number of antennas, the systembandwidth, the PHICH (Physical HARQ Indicator Channel) size etc.

Each CCE consists of 36 REs. However, in order to achieve time andfrequency diversity for the PDCCHs, each CCE and its REs are spread out,both in time over the OFDM symbols used for the control region and infrequency over the configured bandwidth. This is achieved through anumber of operations including interleaving, and cyclic shifts etc.These operations are however completely known to the UEs.

In the preferred embodiment of the invention, the PDCCH space may bedivided, as will be described in more detail below.

FIG. 3 is a flow chart, illustrating a process performed in the eNodeB,in order to determine whether to divide the PDCCH space into multiplegroup subsets. The advantage of dividing the PDCCH space into two ormore group subsets is most noticeable when there are a large number ofCCEs available. This is for two reasons. Firstly, it is mainly whenthere are a large number of CCEs that there will be a capacity problemin the UE. That is, when there are a large number of CCEs, there aremany CCE combinations that, with an undivided PDCCH space, would need tobe decoded by the UE, placing a large load on the UE. Secondly, it ispreferable to avoid resource fragmentation when there are few CCEs.

Thus, the process is advantageously performed whenever the number ofCCEs may change. At start up or at reconfiguration the bandwidth, andhence the number of subcarriers in the system, could change, which isone of many parameters determining the amount of CCEs and hence in turnthe total amount of possible PDCCHs.

In addition, the size of the control region, i.e., the number of OFDMsymbols used for it, is also an important parameter for determining howmany PDCCHs are possible in total. Since this could vary from onesubframe to another, the division of the PDCCH space should preferablyalso vary on a subframe basis. This can be achieved by performing thecomplete process once per subframe. Alternatively, if the number ofdifferent possible divisions of the PDCCH space is not too large, thepossible divisions could be determined at startup of the eNodeB and thenstored for all combinations of bandwidth and control region size, andany other relevant parameters.

Thus, in step 30 of the process illustrated in FIG. 3, the number ofavailable CCEs is determined and, in step 32, this number is comparedwith a threshold number. If the number of available CCEs does not exceedthe threshold number, the process passes to step 34, in which it isdetermined that an undivided PDCCH space should be used. For example,the threshold number of CCEs, below which the undivided PDCCH space isused, may for example be set to about 10 or 15 CCEs. In this case, forexample, every UE must decode every possible PDCCH. In step 35, theeNodeB is then able to transmit PDCCHs to UEs, for example containingresource assignment messages, using this undivided PDCCH space.

If it is determined in step 32 that the number of available CCEs exceedsthe threshold number, the process passes to step 36, in which it isdetermined that a divided PDCCH space should be used, as will bedescribed in more detail below.

Following the division of the PDCCH space, the eNodeB will be able totransmit PDCCHs, for example containing resource assignment messages, toUEs as shown in step 38, again as will be described in more detailbelow.

FIG. 4 is a flow chart, illustrating a process performed in a UE,preferably in each subframe, in order to determine which part of thePDCCH space it must decode.

Thus, in step 50 of the process illustrated in FIG. 3, the number ofavailable CCEs is determined. Specifically, the UE should calculate thenumber of CCEs for each subframe. The number of CCEs in each subframecan easily be calculated from the PCFICH indicator, the configuredbandwidth, PHICH size and duration, number of antennas etc. All ofthese, except the PCFICH, are assumed to be semi-statically configured.

In step 52, the UE determines from the calculated number of CCEs in eachsubframe whether group subsets are used or not. For example, asdescribed above with reference to FIG. 3, the number of CCEs in eachsubframe can be compared with a threshold number. This threshold numbermust of course be the same as the threshold number used by the eNodeB instep 32. The threshold number can be predefined, and stored in theeNodeB and the UE, or it can be signaled from the eNodeB to the UE, forexample in RRC signalling.

If group subsets are not used, the process passes to step 54, in whichit is determined that the UE must decode every possible PDCCH.

If it is determined in step 52 that group subsets are being used, theprocess passes to step 56, in which the UE determines which group subsetto decode. More specifically, the UE should know by some implicitmapping or signaling which group subset to decode. There are severalstraightforward methods that could be utilized to achieve an implicitmapping. One example is modulo counting of the Radio Network TemporaryIdentifier (RNTI) of the UE, in order to determine the starting locationfor the group subset. Of course, the UE must use the same method thatwas used in the eNodeB to allocate UEs to group subsets.

In step 58, the UE decodes the PDCCHs in the relevant group subset,determined in step 56, and in the common subset.

As mentioned above, when the number of available CCEs is above athreshold value, and it is decided to divide the PDCCH space, there areat least two group subsets. It may be advantageous that the number ofgroup subsets that are used grows beyond two with an increasing totalnumber of available CCEs, although the number of group subsets may notgrow in direct proportion with the total number of available CCEs.

However, neither details with respect to number of group subsets nordetails about how a UE is mapped to a certain group subset are essentialfor the invention.

FIG. 5 shows the available CCE resources at one particular time, by wayof example. Thus, there are a number of CCEs, each having a respectiveCCE index, as shown along the horizontal axis in FIG. 5. These CCEs canbe combined with different aggregation levels, as is known. Thus, FIG. 5shows the CCEs 70 with the lowest aggregation level of 1, but also showsthe CCEs in aggregations 72 with an aggregation level of 2, inaggregations 74 with an aggregation level of 4, and in aggregations 76with the highest aggregation level of 8. As is known, the PDCCH spaceincludes all CCEs on all aggregation levels.

According to an exemplary embodiment, one common subset is defined, inaddition to the group subsets mentioned above. This subset of PDCCHs isthen mandatory for all UEs to decode.

In the example shown in FIG. 5, the common subset is defined to containcertain CCEs at a certain aggregation level. The common subset mayadvantageously be formed to cover the largest possible PDCCH size, i.e.8 CCEs in the example shown in FIG. 5. By defining the common subset asall possible PDCCHs on aggregation level 8, more or less the whole CCEspace can be covered with a small set of PDCCHs, and so all CCEs areenabled for use by any UE without forcing each UE to decode a largenumber of PDCCH candidates. By instead defining the common subset toinclude possible PDCCHs on lower aggregation levels, more decodings bythe UE would be required in order to cover a certain CCE space.

Group subsets may for example be formed to cover a certain set of CCEresources corresponding to certain CCE indices. The possible PDCCHswithin each group subset are then defined by the possible aggregationsinto PDCCHs from the CCE indices defined as resources for that groupsubset. All possible PDCCHs on all aggregation levels (i.e., 1, 2, 4,and 8) for all CCE indices of the group may then be defined to be partof that specific group subset.

Thus, the common subset or each common subset will be decoded by everyUE, and each group subset will be decoded only by a limited group ofUEs.

In the example shown in FIG. 5, one group subset is defined to cover allpossible PDCCHs on all aggregation levels (i.e., 1, 2, 4, and 8) for allCCE indices in the range from i1 to iN. This group subset thereforecovers certain CCE indices, namely from CCE index i1 to iN, on each ofaggregation levels 1, 2, 4, and 8.

As an alternative, a group subset may be defined such that it containsCCEs at one aggregation level that do not overlap with the CCEs at adifferent aggregation level. For example, a group subset may be definedso that it covers a first set of CCEs at aggregation level 8 extendingover the first half of the range from i1 to iN (i.e. from i1 to i[N/2]and a second set of CCEs at aggregation level 4 extending over the upperhalf of the range from i1 to iN (i.e. from i[N/2+1] to iN).

Thus, in order to avoid the need to send PDCCHs for broadcast messagesin all group subsets, a common subset is utilized for broadcastmessages. Since, in the illustrated embodiment, the common subsetincludes the PDCCHs containing the larger number of CCEs, these are wellsuited for broadcast messages which typically need to cover the wholecell. By utilizing the common subset for broadcasting, huge savings areachieved in terms of CCE resources, since the same assignment wouldotherwise have to be sent in many different group subsets and in each ofthem probably occupy a large number of CCEs in order to cover the cell.

The definition of the common subset allows messages to be allocated toPDCCHs in an efficient manner. In the case where most of the users at agiven time are utilizing the same group subset, then the most expensivePDCCHs, i.e., the PDCCHs containing many CCEs, can be moved to PDCCHswhich are part of the common subset. By doing this, several smallerPDCCHs, i.e., PDCCHs consisting of only a few CCEs, are made free. Inthis way unwanted skewed distributions, with respect to the number ofusers utilizing the different group subsets, can be handled in anefficient way where the complete PDCCH resource can potentially still beutilized. For example, where a message, that is to be sent to onespecific UE, requires many CCEs, that message can be sent on a PDCCH inthe common subset. This will still ensure that the specific UE willdecode the message, and will allow the PDCCHs in the group subset to beused for sending smaller messages to the UEs that will decode that groupsubset.

In order to make the solution even more flexible, an optional upgrade ofPDCCHs occupying fewer CCEs per PDCCH compared to the PDCCHs in thecommon subset is introduced. This means that the number of CCEs perPDCCH can be increased to an aggregation level above what is needed inorder to adapt to the link. As a result, PDCCHs, no matter the requiredsize in terms of number of CCEs, can be upgraded to an aggregation levelcorresponding to 8 CCEs (or whatever is the largest aggregation levelset in the standard) for a PDCCH. Hence, any PDCCH, no matter therequired aggregation level or which UE it is aimed for, can potentiallybe moved to cover any CCE index.

For example, in the case where a group subset is defined in such a waythat it contains CCEs at one aggregation level that do not overlap withthe CCEs at a different aggregation level, and in the situation where itis desired to transmit a PDCCH requiring a low aggregation level (forexample aggregation level 2) but all possible PDCCHs at that lowaggregation level are occupied, then that PDCCH can be transmitted at ahigher aggregation level (for example aggregation level 4) usingdifferent CCEs within the group subset.

There is thus disclosed a method for allocating communicationsresources.

The present invention may, of course, be carried out in other ways thanthose specifically set forth herein without departing from essentialcharacteristics of the invention. The present embodiments are to beconsidered in all respects as illustrative and not restrictive, and allchanges coming within the meaning and equivalency range are intended tobe embraced therein.

1. A method of allocating communications resources in atelecommunication system, in which the assignments of resources to userequipments are transmitted in a control region of each downlinksubframe, the control region comprising a plurality of downlink controlchannels, the method comprising: dividing the downlink control channelsinto at least one common subset of the downlink control channels and aplurality of group subsets of the downlink control channels, in such away as to enable every user equipment to decode the common subset andonly one group subset.
 2. A method as claimed in claim 1, wherein thecommon subset comprises downlink control channels on the highestavailable aggregation level.
 3. A method as claimed in claim 1, whereinthe common subset comprises all possible downlink control channels onone aggregation level.
 4. A method as claimed in claim 3, wherein thecommon subset comprises all possible downlink control channels on thehighest aggregation level.
 5. A method as claimed in claim 1, whereineach group subset comprises downlink control channels on one or moreaggregation levels covering a subset of control channel elements.
 6. Amethod as claimed in claim 5, wherein each group subset comprises allpossible downlink control channels on all aggregation levels coveringthe subset of control channel elements.
 7. A method as claimed in claim1, further comprising: transmitting broadcast messages on at least onedownlink control channel forming part of the common subset of thedownlink control channels.
 8. A method as claimed in claim 1, furthercomprising: transmitting a resource assignment message for a userequipment on at least one downlink control channel forming part of therespective group subset of the downlink control channels.
 9. A method asclaimed in claim 1, wherein a respective group subset for a userequipment is determined by modulo counting of a RNTI of the userequipment.
 10. A method as claimed in claim 1, further comprising:transmitting a resource assignment message for a user equipment on atleast one downlink control channel forming part of the common subset ofthe downlink control channels.
 11. A method as claimed in claim 1,further comprising transmitting a message on a downlink control channelcomprising a larger number of control channel elements than required forthe message.
 12. A method of operation of a user equipment in order todetermine communications resources allocated thereto in atelecommunication system, in which the assignments of resources to userequipments are transmitted in a control region of each downlinksubframe, the control region comprising a plurality of downlink controlchannels, the method comprising: determining a division of the downlinkcontrol channels into at least one common subset of the downlink controlchannels and a plurality of group subsets of the downlink controlchannels; determining a relevant group subset from the plurality ofgroup subsets; and decoding the downlink control channels forming thecommon subset or each common subset of the downlink control channels,and decoding only the downlink control channels of the relevant groupsubset of the downlink control channels.
 13. A method as claimed inclaim 12, wherein the step of determining the division of the downlinkcontrol channels into at least one common subset of the downlink controlchannels and a plurality of group subsets of the downlink controlchannels comprises: determining a number of control channel elements ineach subframe; and determining from said number of control channelelements in each subframe whether a division into two or more groupsubsets has been done.
 14. A method as claimed in claim 12, wherein thestep of determining the relevant group subset of the downlink controlchannels comprises modulo counting of the RNTI.
 15. A method as claimedin claim 12, wherein the downlink control channels are PDCCH:s.
 16. Anetwork node for a telecommunication system, in which the assignments ofresources to user equipments are transmitted in a control region of eachdownlink subframe, the control region comprising a plurality of downlinkcontrol channels, the network node being adapted to allocatecommunications resources by: dividing the downlink control channels intoat least one common subset of the downlink control channels and aplurality of group subsets of the downlink control channels, enablingevery user equipment to decode the common subset and only one groupsubset.
 17. A network node as claimed in claim 16, wherein the commonsubset comprises downlink control channels on the highest availableaggregation level.
 18. A network node as claimed in claim 16, whereineach group subset comprises downlink control channels on one or moreaggregation levels covering a subset of control channel elements.
 19. Anetwork node as claimed in claim 16, further adapted to: transmitbroadcast messages on at least one downlink control channel forming partof the common subset of the downlink control channels.
 20. A networknode as claimed in claim 16, further adapted to: transmit a resourceassignment message for a user equipment on at least one downlink controlchannel forming part of the common subset of the downlink controlchannels.
 21. A network node as claimed in claim 16, wherein arespective group subset for a user equipment is determined by modulocounting of a RNTI of the user equipment.
 22. A network node as claimedin claim 16, wherein the network node is an eNodeB of an Evolved RadioAccess Network.
 23. A network node as claimed in claim 16 wherein thedownlink control channels are PDCCH:s.
 24. A user equipment in atelecommunication system, in which the assignments of resources to userequipments are transmitted in a control region of each downlinksubframe, the control region comprising a plurality of downlink controlchannels, the user equipment being adapted to determine communicationsresources allocated thereto by a method comprising: determining adivision of the downlink control channels into at least one commonsubset of the downlink control channels and a plurality of group subsetsof the downlink control channels; determining a relevant group subsetfrom the plurality of group subsets; and decoding the downlink controlchannels forming the common subset or each common subset of the downlinkcontrol channels, and decoding only the downlink control channels of therelevant group subset of the downlink control channels.
 25. A userequipment as claimed in claim 24, wherein the step of determining thedivision of the downlink control channels into at least one commonsubset of the downlink control channels and a plurality of group subsetsof the downlink control channels comprises: determining a number ofcontrol channel elements in each subframe; and determining from saidnumber of control channel elements in each subframe whether groupsubsets are used.
 26. A user equipment as claimed in claim 24, furtheradapted to determine the relevant group subset of the downlink controlchannels by modulo counting of the RNTI.
 27. A user equipment as claimedin claim 24, wherein the downlink control channels are PDCCH:s.